Disc brake caliper, method for manufacturing a caliper and caliper spring

ABSTRACT

A disc brake caliper has a caliper body and a pair of pads and, in each side portion of the caliper body, a distal piston and a proximal piston, having radially distanced and aligned pressure centers.

The present invention relates to the field of braking systems for vehicles, and in particular the present invention relates to a disc brake caliper.

Very briefly, a disc brake consists of a disc, which is integral in rotation with the vehicle wheel, and a fixed caliper, in which a pair of pads carrying friction material are housed. The caliper also holds pistons which, by being hydraulically operated, push the pads against the disc surfaces, thus obtaining the braking by virtue of the action of the friction material.

The number and relative position of the pistons considerably influence the action of the disc brake; for example, important factors depend on them, such as caliper rigidity, from which a more or less prompt braking derives, friction material consumption evenness, and the like.

SUMMARY OF THE INVENTION

It is the object of the present invention to obtain a disc brake caliper capable of obtaining a particularly prompt and immediate braking.

Such an object is achieved by a caliper made according to claim 1. The claims dependent thereon describe variant embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the caliper according to the present invention will be apparent from the following description, given by way of non-limiting example, according to the accompanying drawings, in which:

FIG. 1 shows a disc brake caliper according to an embodiment of the present invention;

FIG. 2 shows a plan view of the caliper in FIG. 1;

FIG. 3 shows a pad engaged with pistons of the caliper in FIG. 1;

FIG. 4 shows a rear front view of the pad with pistons in FIG. 3;

FIG. 5 shows a diagram highlighting the position of the center of gravity of the bridge portions and of the center of gravity of the piston areas in the caliper in FIG. 1;

FIG. 6 shows the pressure distribution in a pad of a caliper according to the present invention, while FIG. 7 shows the pressure distribution in a pad of a caliper according to the prior art;

FIG. 8 shows a lost core for making a caliper body of a caliper according to a further aspect of the present invention;

FIGS. 9 and 10 show semi-finished caliper bodies according to the present invention;

FIG. 11 shows pads coupled with return springs according to another aspect of the present invention;

FIG. 12 shows a section of the pads with return springs in FIG. 11; and

FIGS. 13 and 14 show the return spring in FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the accompanying figures, reference numeral 1 indicates a disc brake caliper according to an embodiment of the present invention, intended to be arranged straddling a disc rotatable about a rotation axis Z.

Hereinafter, the expressions “axial direction” or “axially” will be used with reference to a direction parallel to the rotation axis Z of the disc, the expressions “radial direction” or “radially” will be used with reference to a radial direction with respect to the rotation axis and the expressions “circumferential direction” or “circumferentially” will be used with reference to a circumferential pattern about the rotation axis.

The caliper 1 comprises a caliper body 2, usually monolithic, preferably made by gravity casting.

The caliper body 2 consists of:

-   -   a first side portion 2 a and a second side portion 2 b, which         when the caliper is coupled to the disc have prevailing         extension along the circumferential direction and border the         surfaces of the disc;     -   a front bridge portion 4 a and a rear bridge portion 4 b, placed         at circumferential ends of the side portions 2 a, 2 b and         straddling the disc;     -   an upper axial portion 6 a, placed straddling the disc, which         joins the first side portion 2 a and the second side portion 2         b, has predominantly axial extension and is placed in an         intermediate position between the front portion 4 a and the rear         portion 4 b; and     -   an upper circumferential portion 6 b, which joins the front         portion 4 a and the rear portion 4 b, has predominantly         circumferential extension and is placed in an intermediate         position between the first side portion 4 a and the second side         portion 4 b.

The upper portions 6 a, 6 b intersect in a central portion 8, making a cross body consisting of axial arms 6 a′, 6 a″ and circumferential arms 6 b′, 6 b″.

Preferably, each axial arm 6 a′, 6 a″ is tapered from the respective side portion 2 a, 2 b towards the central portion 8.

Piston chambers, accommodating therein a respective piston, which can be hydraulically actuated by means of pressurized oil fed by means of a hydraulic circuit, also prevalently obtained in the pump body, are obtained within the pump body 2, and in particular in the side portions 2 a, 2 b thereof.

The caliper 1 further comprises a pair of pads 20, accommodated in the caliper body 2, supported in slidable manner so as to allow an axial sliding under the bias of the pistons.

Preferably, the caliper according to the present invention has eight pistons, operating in fours on a respective pad.

In particular, the pad 20 can be biased by an intermediate distal piston 22 a, by an intermediate proximal piston 22 b, by a front side piston 24 a and by a rear side piston 24 b.

Having identified the rotation axis Z of the disc, the pressure centers 24 a′, 24 b′ of the side pistons 24 a, 24 b lie on an imaginary circumference I centered on the rotation axis Z, at a predetermined angular distance A, while the pressure centers 22 a′, 22 b′ of the intermediate pistons 22 a, 22 b are contained angularly in the angular region identified by the angular distance A.

Preferably, the pressure center 22 a′ of the first intermediate piston 22 a lies on the bisector B which bisects the angular region identified by the angular distance A, at a first radial distance Ra from the rotation axis Z; for example, the pressure center 22 a′ of the distal intermediate piston 22 a lies on the imaginary circumference I.

Furthermore, according to the invention, the pressure center 22 b′ of the proximal intermediate piston 22 b lies on the bisector B, at a second radial distance Rb from the rotation axis Z, smaller than the first radial distance Ra.

In other words, the pressure center 22 a′ of the distal intermediate piston 22 a and the pressure center 22 b′ of the proximal intermediate piston 22 b are distanced and radially aligned along a radial direction R.

With respect to the pad 20, the pressure centers 22 a′, 22 b′, 24 a′, 24 b′ fall within the contour of the pad, preferably at the vertexes of an imaginary rhombus for which the minor diagonal is arranged radially. Preferably, the entire sections of the pistons 22 a, 22 b, 24 b, 24 b fall within the contour of the pad.

Having positioned the pad 20 in the caliper pump body 2, the central portion 8 of the caliper body 2 intersects the radial direction R of the pressure centers 22 a′, 22 b′ of the intermediate pistons 22 a, 22 b, preferably symmetrically, while the front bridge portion 4 a and the rear bridge portion 4 b are arranged circumferentially externally to the pressure centers 24 a′, 24 b′ of the side pistons 24 a, 24 b (FIG. 5).

Advantageously, the center of gravity of the front bridge portion 4 a, of the rear bridge portion 4 b and of the central portion 8 is close to the center of gravity of the pistons 22 a, 22 b, 24 a, 24 b, thus resulting in a particularly rigid caliper, i.e. capable of developing a particularly prompt and vigorous braking.

Furthermore, advantageously during braking, the load distribution on the pad is particularly uniform (FIG. 6) with respect to the distribution of a usual pad of the prior art (FIG. 7). This allows, in the caliper according to the invention, to reduce the anomalous, non-uniform consumption of the friction material and to improve the braking action.

According to a further aspect of the invention, during the casting of the caliper body according to the present invention, a lost core 30 is used, consisting of a cross-shaped core body 31, intended to obtain in the caliper body the space for housing the pads, from which the intermediate chamber cores 32 a, 32 b for making the chambers for the intermediate pistons 22 a, 22 b, and the side chamber cores 34 a, 34 b for making the chambers for the side pistons 24 a, 24 b axially protrude, on one side and on the other (FIG. 8).

Preferably, the core 30 includes at least one circuit branch core which connects at least two piston chamber cores for making a circuit branch of the pressurized oil feeding circuit.

In particular, the core 30 has a proximal branch core 36 which protrudes from the proximal piston chamber core 32 b and extends towards the distal piston chamber core 32 a and a distal branch core 38 which protrudes from the distal piston chamber core 32 a and extends towards the proximal piston chamber core 32 b.

The proximal branch core 36 and the distal branch core 38 terminate with a respective free end 40, 42 which are very close to each other but separated. In other words, the proximal branch core 36 and the distal branch core 38 are separate from each other, also on the tip.

From the casting, after having eliminated the core 30, a semi-finished caliper body 50 is obtained, which is provided, in the side portion 2 a, 2 b, with the proximal piston chamber 52 and with the distal piston chamber 54 for housing the proximal intermediate piston 22 b and the distal intermediate piston 22 a, respectively, and with the front piston chamber 56 and with the rear piston chamber 58 for housing the front side piston 24 a and the rear side piston 24 b, respectively (FIG. 9).

Furthermore, a proximal circuit branch 60 extends from the proximal piston chamber 52 towards the distal piston chamber 54 and a distal circuit branch 62 extends from the distal piston chamber 54 towards the proximal piston chamber 52.

In the semi-finished caliper 50, the proximal circuit branch 60 does not intercept the distal circuit branch 62, i.e. said branches 60, 62 are separate, as the respective branch cores 36, 38 were.

The semi-finished caliper 50 is subjected to processing by material removal, in particular a first hole is made to remove the material from the caliper body which separates the proximal circuit branch 60 from the distal circuit branch 62, thus putting them into communication (FIG. 10).

Preferably, a second hole is further made to put the front piston chamber 56 into communication with the rear piston chamber 58, preferably at the same time as the first hole is made, along the same perforation axis F.

A semi-finished perforated caliper body 70 is thus obtained, in which the proximal piston chamber 52 is connected to the distal piston chamber 54 by means of the proximal branch 60 and the distal branch 62 obtained in the caliper body 2, while the front piston chamber 56 is connected to the rear piston chamber 58 by means of a connection pipe 72 which also intercepts the proximal branch 60 and/or the distal branch 62.

The connection branch 72 leads onto the front portion 4 a with a front gap 74 and onto the rear portion 4 b with a rear gap 76, intended to be plugged. The front gap 74 on one side of the caliper body 2 is instead intended to be connected to the front gap 74′ of the other side of the caliper body through a bridge pipe 78, generally constituted by a tube, applied externally to the caliper body 2 (FIG. 1).

According to another aspect of the present invention, the pads 20 are permanently biased towards the respective rest position by at least one spring 80, preferably by a pair of identical springs 80, preferably obtained by bending an appropriately shaped steel sheet.

A pad 20 comprises a supporting plate 21, having an outer surface 23 intended for the action of the pistons, and an opposite inner surface 25, and friction material carried by the supporting plate 21 on the inner surface 25.

The supporting plate 21 has a proximal edge 27, at which eyelets 29 are obtained for supporting the pad 20 in sliding manner, sides 31, 33, and a distal edge 35, to which the spring 80 is applied.

The spring 80, which operates on both pads 20 at the same time, comprises a central strip 82 which extends axially, when the spring 80 is applied to the caliper body 2, between the pads 20, straddling the disc.

The central strip 82 is folded at the ends so as to form, for each end, a curl 84, which then extends on an abutment plane 86, intended to come into contact with the distal edge 35 of the pads 20.

The spring 80 further comprises a coupling portion 88 arranged centrally, comprising two pairs 90 of wings 92; the two pairs 90 are arranged side by side to the strip 82, in a stretch thereof which forms a recess 94.

Innovatively, the caliper according to the present invention is particularly rigid, and thus allows to apply prompt, vigorous braking; such a behavior is conferred, moreover, by the arrangement of the pistons, which determine a center of gravity very close to the center of gravity of the bridge portion sections.

Furthermore, the consumption of friction material, as well as the pressure distribution on the braking band, is advantageously even.

According to a further advantageous aspect, the manufacturing process of the brake caliper is very reliable, and in particular the making of a hole on the semi-finished caliper body for forming the hydraulic connection between the piston chambers prevents the core from having weakened portions which could be easily subject to breakage during casting.

It is apparent that a person skilled in the art may made changes to the caliper described above, all of which are contained within the scope of protection as defined in the following claims, in order to satisfy contingent needs. 

The invention claimed is:
 1. A caliper for a disc brake applicable to a disc rotatable about a rotation axis, comprising: a caliper body having a first side portion and a second side portion, having a prevailing extension in a circumferential direction, and a front bridge portion and a rear bridge portion, circumferentially spaced and placed at circumferential ends of the side portions to join them, said front bridge portion and said rear bridge portion defining a caliper body center of gravity between them; a pair of pads having friction material supported by the caliper body to be arranged on one side and the other side of the disc, in an axially slidable manner; in each side portion, a distal piston and a proximal piston, supported by the caliper body for influencing the pad, have pressure centers that are radially spaced and aligned, wherein in each side portion, a front side piston and a rear side piston, supported by the caliper body for influencing the pad, have pressure centers that are laterally spaced and aligned, wherein the pressure centers for each of the pistons fall at vertices of an imaginary rhombus for which a minor diagonal is disposed radially and a major diagonal is disposed laterally, wherein said minor diagonal intersects said major diagonal of the imaginary rhombus at a midpoint of the imaginary rhombus; wherein said caliper body center of gravity is laterally and radially adjacent a center of gravity of said pistons, wherein each side portion has a total of only four pressure centers.
 2. The caliper according to claim 1, further comprising, in each side portion, said front side piston and said rear side piston, have said pressure centers lying on an imaginary circumference centered on the rotation axis, at a defined angular distance, and the pressure centers of the proximal and distal pistons are angularly contained in an angular region identified by the angular distance.
 3. The caliper according to claim 2, wherein the pressure center of the distal piston and the pressure center of the proximal piston lie on a bisector bisecting the angular region identified by the angular distance.
 4. The caliper according to claim 2, wherein the pressure centers fall within the peripheral contour of each pad of the pair of pads.
 5. The caliper according to claim 2, wherein said pressure centers are arranged so that said major diagonal extends between said front side piston and said rear side piston without intersecting with said distal piston or said proximal piston.
 6. The caliper according to claim 2, wherein entire sections of the pistons fall within a peripheral contour each pad of the pair of pads.
 7. The caliper according to claim 1, wherein the caliper body comprises: an upper axial portion that joins together the two side portions has a predominantly axial extension and is placed in an intermediate position between the front portion and the rear bridge portion; and an upper circumferential portion, which joins the front portion and the rear bridge portion, has a predominantly circumferential extension and is placed in an intermediate position between the two side portion; wherein the upper axial portion and the upper circumferential portion intersect in a central portion, realizing a cross body consisting of axial arms and circumferential arms.
 8. The caliper according to claim 7, wherein each axial arm has a shape tapered from the respective side portion towards the central portion.
 9. The caliper according to claim 7, wherein the central portion of the caliper body symmetrically intersects the radial direction of the pressure centers of the distal and proximal pistons.
 10. The caliper according to claim 7, wherein the front bridge portion and the rear bridge portion are placed circumferentially externally to the pressure centers of the side pistons.
 11. A caliper for a disc brake applicable to a disc rotatable about a rotation axis, comprising: a caliper body having a first side portion and a second side portion, having a prevailing extension in a circumferential direction, and a front bridge portion and a rear bridge portion, circumferentially spaced and placed at circumferential ends of the side portions to join them; a pair of pads having friction material supported by the caliper body to be arranged on one side and the other side of the disc, in an axially slidable manner; in each side portion, a distal piston and a proximal piston, supported by the caliper body for influencing the pad, have pressure centers that are radially spaced and aligned, wherein in each side portion, a front side piston and a rear side piston, supported by the caliper body for influencing the pad, have pressure centers that are laterally spaced and aligned, wherein the pressure centers for each of the pistons fall at vertices of an imaginary rhombus for which a minor diagonal is disposed radially and a major diagonal is disposed laterally, wherein said minor diagonal intersects said major diagonal of the imaginary rhombus at a midpoint of the imaginary rhombus; wherein each side portion has a total of only four pressure centers.
 12. The caliper of claim 11, wherein there are no pistons radially above or below the front side piston or the rear side piston.
 13. The caliper of claim 11, wherein said pads have a perimeter defining a rhombus shape.
 14. The caliper of claim 11, wherein said caliper body is a cast body. 